Anticancer activity profiling of parthenolide analogs generated via P450-mediated chemoenzymatic synthesis

Abstract

The plant-derived sesquiterpene lactone parthenolide (PTL) was recently found to possess promising anticancer activity but elaboration of this natural product scaffold for optimization of its pharmacological properties has proven challenging via available chemical methods. In this work, P450-catalyzed C-H hydroxylation of positions C9 and C14 in PTL was coupled to carbamoylation chemistry to yield a panel of novel carbamate-based PTL analogs ('parthenologs'). These compounds, along with a series of other C9- and C14-functionalized parthenologs obtained via O-H acylation, alkylation, and metal-catalyzed carbene insertion, were profiled for their cytotoxicity against a diverse panel of human cancer cell lines. These studies led to the discovery of several parthenologs with significantly improved anticancer activity (2-14-fold) compared to the parent molecule. Most interestingly, two PTL analogs with high cytotoxicity (LC₅₀∼1-3μM) against T cell leukemia (Jurkat), mantle cell lymphoma (JeKo-1), and adenocarcinoma (HeLa) cells as well as a carbamate derivative with potent activity (LC₅₀=0.6μM) against neuroblastoma cells (SK-N-MC) were obtained. In addition, these analyses resulted in the identification of parthenologs featuring both a broad spectrum and tumor cell-specific anticancer activity profile, thus providing valuable probes for the future investigation of biomolecular targets that can affect cell viability across multiple as well as specific types of human cancers. Altogether, these results highlight the potential of P450-mediated chemoenzymatic C-H functionalization toward tuning and improving the anticancer activity of the natural product parthenolide.

Keywords: Anticancer activity; Chemoenzymatic synthesis; Cytochrome P450(BM3); Enzymatic hydroxylation; Late-stage C–H functionalization; Parthenolide; Sesquiterpene lactones.

Figure 1

Marketed drugs containing carbamate moieties.

Figure 2

Cytotoxicity of PTL and of the parthenologs against the panel of cancer cell lines at the standard dose of 10 μM (n = 5). Standard deviation is within 10%. Reported values corresponds to: (% cell viability)/100. See Table S1 for complete data and for cytotoxicity data against Jurkat and JeKo-1 cells at the lower compound dose (2 μM).

Figure 3

X-ray crystal structure of compound 14.

Scheme 1

Chemoenzymatic synthesis of C9- and C14-functionalized PTL analogs via P450-catalyzed hydroxylation and carbamoylation chemistry. (a–b) 1 mM parthenolide, cell lysate containing ~ 0.1 mol% P450 and ~ 2 μM PTDH, 150 μM NADP⁺, 50 mM sodium phosphite in 50 mM potassium phosphate buffer (pH 8.0), room temperature, 14 hours. P450 variant II-C5 was used for (a), and P450 variant FL#46 for (b); (c) R–NCO, DBTDL, DCM, room temperature (3–12 hours).

Scheme 2

Synthesis of C9- and C14-functionalized PTL analogs via acylation, alkylation and O-H carbene insertion chemistry.